Direct Rendering Infrastructure 3 is new to X.Org Server 1.15, which will officially be released soon. DRI3 provides some notable benefits for enhancing the desktop Linux experience on X.Org. Up to now though only the Intel Mesa driver has supported DRI3, but Keith has baked up a DRI3 Gallium3D patch-set.
Hitting the mailing list on Friday were a set of eighteen patches that provide DRI3 clean-ups and fixes along with the code to finish the DRI3 support inside Mesa's Gallium3D area. This work involves some fixes, adding GLX_INTEL_swap_event support, __DRIimageDriverExtension support, and other changes for namely being able to support the Radeon and Nouveau drivers on Direct Rendering Infrastructure 3 when also using X.Org Server 1.15+ and other updated X packages.
More details on the Mesa-dev list.